Devices for separating solid objects from a stream of water to be used in cooling a power-generating plant generally comprise a substantially cylindrical separator housing, a radially oriented inlet channel, a filtrate-outlet conduit or pipe connected to the bottom of the housing and an outlet conduit attached to a cylindrical wall of the housing for drawing off the filtered-out solid objects. A cylindrical sieve disposed in the housing forms therewith a substantially annular outer filter chamber communicating with the inlet channel and the solids-outlet conduit, while the space inside the filter sieve communicates with the filtrate-outlet pipe. A gating or valve flap is provided in the inlet channel proximate to the housing for regulating the velocity and mass flow of the incoming stream.
As described and illustrated in German patent document (Auslegeschrift) No. 2,058,395, a single valve flap is swingably mounted in the inlet channel proximate to the junction of the same and the housing for pivoting about an axis parallel to a vertically extending axis of symmetry of the filter sieve, the solids-outlet conduit being attached to the cylindrical housing wall substantially tangentially thereto and to the annular outer filter chamber. A pair of guide plates spaced from the valve flap may be rigidly fixed thereto, as shown and described in German patent document (Auslegeschrift) No. 2,225,727 for directing the incoming water stream in a tangential direction with respect to the filter sieve and for accelerating the water to a minimum velocity preferably greater than two meters per second. At inlet stream velocities less than two meters per second, the cleaning effects precipitously decrease.
Because of the tangential orientation of the solids-outlet conduit, there is a preferred direction and path of fluid flow, whereby different portions of the outer surface of the sieve cannot be equally well cleaned of adhering objects such as mussels. Furthermore, the annular motion of the incoming water stream about the filter sieve causes a whirlpool or vortex therein, this vortex leading to pressure and energy losses and yet in no way contributing to the cleaning of the sieve. To reduce these pressure losses in practice, the valve flap is generally maintained in an intermediate position and is pivoted for short intervals to effect an intermittent sieve cleaning.
In such a method of separator operation, difficulties arise if the number of solid objects in the arriving fluid stream suddenly increases, such as if a school of fish swims into the inlet conduit or a bank of mussels drops from the conduit walls. In such situations, the filter is blocked before the valve flap can be pivoted to a cleaning position.
Another disadvantage of conventional separators is the injury and killing of fish, owing to the discontinuous separator operation and to the high stream velocities involved.